In one apparatus (East German Pat. No. 59 536) a bushing provided with a helical rib is fastened eccentrically on a support which rotates around the longitudinal axis of the pipe to be corrugated. In this device the bushing is fastened on the support at an angle to the longitudinal axis of the pipe, whereby a sufficiently deep corrugation is produced.
A similar device (West German OS No. 19 00 953) consists of a bushing with threading which is also fastened eccentrically on a support which rotates around the longitudinal axis of the pipe.
The two devices have the feature in common that the inside diameter of the corrugation tool or bushing is larger than the outside diameter of the pipe to be corrugated. Since in both devices the bushings are fastened in a freely rotatable manner and eccentrically on the carrier, the bushings roll on the surface of the pipe upon rotation of the carrier and sufficient eccentricity and thereby produce the annular parallel corrugation.
It has, however, been found that the corrugation produced with the known devices is not suitable for many purposes of use since it is not uniform over the length of the pipe. Thus, for instance, a corrugation which is completely equal or the same over the length of the pipe is necessary for application in high-frequency electromagnetic wave technology. Furthermore, the corrugation should be free of deformations in the region of the flanks of the corrugations and be as close as possible to a sinusoidal curve form. Also a helical corrugation cannot be produced with these devices.